Elevator controls



2 Sheets-Sheet 2 J. H. BORDEN ELEVATOR CONTROLS MT-I mvrsmozg. JOSEPH H v BOR DE N LU-l BY 2 'A 'romue s Nov. 24, 1959 Filed Jan. 15, 1958 L U LD-2 United States Patent 2,914,138 ELEVATOR CONTROLS Joseph H. Borden, Toledo, Ohio, assignor to Toledo Scale Corporation, Toledo, Ohio, a corporation of Ohio Application January 15, 1958, Serial No. 709,041 14 Claims. (Cl. 187-29) This invention relates to elevator controls and more particularly to controls for stopping elevator cars.

Considerable effort has been expended to avoid uneven or excessively rapid stops which create unpleasant sen.-

sations in elevator cars. In present day practice many of the high quality systems effect a substantial portion.

of the deceleration of an elevator car by means of con trol of the lifting mechanism whereby the lifting motor is gradually slowed to a low leveling speed at which point the brakes of the car are applied. Some. systems apply.-

the brakes only after the car has attained the leveling positions and endeavor to terminate all car motion at the time the brake is applied.

permitting some slip until the car levels at the floor. Some difficulty has been experienced in the operation of the preset brakes attributable to the difliculty in main.-.

The practice in the past which has often been utilizedto enhance, the degree of control in operating preset brakes has involved limiting the capacity of the brake to a level only slightly in excess of that required for the rated capacity of the car with which it is associated. In this type of system the car is counterweighted, for example, at 40 percent of capacity load, and accordingly the brake capacity need only be slightly in excess the unbalanced loading at capacity, for example, at 60 percent of that load, in order to operate satisfactorily. However, occasionally it has been found that a car will be overloaded so that its brake is insufficient to hold it in the leveling position at a floor. Slip of this nature is confined to a narrow range inasmuch as the motor is actuated to reposition the elevator car as soon as the car has been displaced by any substantial amount.

However, such slippage is sufficient to permit some misi alignment of the sill of the car doorway and the sill of the hatchway door. In view of these occasional overloads and the resultant slippage of the car ithas been found advantageous to utilize, and in some instances safety codes have required, brake having a capacity substantially in excess of the rated capacity of the associated car. Usually a brake having a capacity which is 125 percent of the rated load of the car is employed. This entails an increase in brake capacity of about 42 percent over a brake having the capacity equal to that rated for the car since a car is usually counterweighted at about 40 percent of load. Thus the brake capacity is increased from 60 percent of rated car load to 85 percent ofrated car load or an increase of 42 percent in brake capacity. This substantial increase greatly enhances the.

tendency of the brake shoes to seize on the brake drum and cause the car to stop abruptly in a manner detri! In other systems the. brake is preset, that is it is applied before the car is. stopped and is expected to retard the car gradually by,

mental to high quality service, particularly passenger service. i

In accordance with the above, one object of this invention is to enhance the stopping characteristics of an elevator car.

Another object is to improve the control of elevator car brakes and more specifically to avoid a so-called hard brake in the abrupt stopping of an elevator car incident thereto.

The above objects are attained in accordance with this invention by means of a control for an elevator brake which applies less than the maximum braking force to the lifting mechanism for the car while the car is brought to a stop and thereafter applies the full braking force.

It is common practice to employ dynamic braking in the lifting motor of an elevator to slow it to a stop. Presetting of the brake may supplement the stopping of the car by the motor in some instances. Accordingly, in this specification the brake capacity is measured as the ability of the brake to hold a stationary car. Thus a brake force of percent of capacity refers to a force sufficient to sustain the uncounterweighted portion of a car loaded to its rated capacity when stationary. The concepts of this invention are not confined to this definition of capacity, however, inasmuch as it is to be recognized that some other measure of brake capacity might be employed, for example, a brake arranged to stop a car moving at a given speed within a given distance of travel might be definitive of a capacity brake, particularly in instances where no dynamic braking is employed.

In the specific embodiment of the invention to be discussed, a brake of conventional form is utilized in cooperation with the driving mechanism for the elevator car whereby a braking operation is effected with a brake drum mechanically coupled to the car lifting mechanism, by engaging a brake shoe with the drum. A unique control of the relationship of the brake shoe to the brake drum during the stopping cycle is afforded. Early in a stopping cycle for the car, the force separating the brake shoe from its drum is reduced substantially, as to a level just sufiicient to maintain the shoe and drum outof engagement. As the car proceeds further toward the landing at which it is to stop, the forces tending to hold the brake shoe off of the drum are reduced below the level necessary to maintain those elements out of engagement but advantageously substantially above the the level utilized in effecting the stopping of the car in order to avoid any seizing of the brake drum by the brake shoe while the car moves slowly in approaching the floor level. These forces partially seat the brake shoe and aid the braking forces of the lift motor. During the final leveling, for example in a zone within about three inches of the floor, the forces tending to relieve the pressure of the brake shoe on the brake drum are momentarily increased to a level which avoids any seizing of the drum by the shoe at low leveling speeds. These relieving forces are restricted to a level insufficient to lift the shoe completely free of the drum. At the time the elevator car attains its stopping position, the force urging the brake shoe against the brake drum is increased to a level sufficient to hold the car when the lifting motor is deenergized. Conveniently this level can be slightly in excess of 100 percent of car capacity. At this moment, a timing operation is initiated and at the termination of that operation the forces tending to relieve the brake shoe from the brake drum are removed completely to set the brake at its maximum capacity usually about percent of rated car capacity. Thus, the car is brought to a stop by a combination of lifting motor operation and the gradual application of braking forces, and the total braking force available is applied only after it has been brought to a stop.

The invention and the above and other objects and features thereof will be more fully appreciated from the following detailed description when read in conjunction with the accompanying drawings wherein:

Figure I is a view of a brake shoe, a mounting, and a fragment of a brake drum taken along the drum axis; for a brake particularly adapted for utilization in accordance with this invention;

Fig. II is an enlarged section of Fig. I taken along the line IIII; and

Fig. III is a circuit diagram showing in schematic manner the relationship between the lifting motor, brake and control mechanisms for the brake insofar as they are necessary to an understanding of the invention.

It is to be appreciated that the brake control of this invention is applicable to many forms of elevator controls and accordingly neither this description nor the accompanying claims should be read as limiting the use of this invention toany particular form of elevator system. For example, this control conveniently lends itself to integration with the elevator system disclosed in R. A. Burgy patent application Serial No. 683,327, which was filed September 11, 1957, and is entitled Elevator Controls.

In the system schematically represented in Fig. I, an elevator car, not shown, serves a plurality of landings, not shown, which may include dispatching terminals, not shown, and intermediate landings. The car and landings are provided with conventional call registering means, not shown, which when operative actuate controls which cause a car to stop at a landing while traveling in the direction for which service is indicated and if no such travel is current to institute such travel whereby the demands for service are answered. This brake control is applicable to either fully automatic or attendant controlled systems.

Each car in a typical elevator system embodying the invention, as shown in Fig. III, is provided with a lifting motor 11 coupled by an armature shaft 12 to a lifting mechanism schematically illustrated as of the gearless type wherein a cable sheave 13 is coupled to shaft 12 and has trained thereover a plurality of lifting cables 14 extending down the hatchway to the elevator car (not shown). A brake drum 15 is also mechanically coupled to cable sheave 13 as by a direct coupling to shaft 12 in the illustration. One or more brake shoes 16 are urged into engagement with brake drum 15 by means of springs 17 and are pulled away from the brake drum 15 in opposition to the biasing force of springs 17 by a solenoid assembly 18. A preferred brake structure which has been employed to advantage with the control circuits of this invention is disclosed in Figs. I and II and will be discussed presently.

A floor selector machine, not shown, is utilized to effect many of the controls which operate in synchronism with effective car position. One form of floor selector is provided with a brush carrying crosshead which advances brushes across a panel array of contacts arranged generally in rows for each landing served by the elevator car and in columns for the several functions to be performed at those landings. An advance motor 19 is arranged to drive the floor selector crosshead over intervals from the instant a car is started away from the landing to the instant the crosshead encounters a landing for which a car or a floor signal has been registered. This drive is efiected through advance motor shaft 21 by means of a coupling schematically represented as a gear 22 on shaft 21. Acceleration and deceleration of the car by means of the lifting motor is effected by an array of cams, only one, .23, of which is shown. This form of control is disclosed in Joseph H. Borden Patent 2,685,348 which issued August 3, 1954, and is entitled Elevator Control System.

Cam 23 is actuated by means of a differential drive 24 from elevator lift motor 11 and advancer motor 19 whereby the output of the differential derived from shaft 25 advances the cam 23 and its associated motor control elements during the initial portion of an operating cycle by virtue of the lead of floor selector crosshead drive motor 19 over the slowly started elevator drive motor 11. This lead persists until the elevator drive motor gets up to speed and thereafter the advance motor maintains essential synchronism with the drive motor. During this advance of the differential, the accelerating force imposed by motor 19 is gradually increased and as the speed of the motor shaft 12 maches and even exceeds the speed of shaft 21, as they are effective in differential 24, certain of said accelerating controls are disabled to hold the car at its designed operating speed. Similarly, when a call is picked up on the floor selector and the crosshead is stopped by stopping advance motor 19 the diiferential output 25 is driven backwards to successively actuate controls which slow the speed of the elevator car and bring it into a leveling Zone adjacent the landing at which it is to stop thereby returning the cam 23 to its position as shown in Fig. I.

In order to insure the maintenance of synchronism between the position of the crosshead on the floor selector and the position of the elevator car in its hatchway and overcome the effects of stretching the cables 14 or slippage of the cables on the lift motor sheave 13, the position of the difierential is corrected to zero at each landing stop of the elevator car by means of a correcting motor 26 which is coupled to the lift motor input for differential 24 through a gear train 27 and slips that input with respect to the shaft 12 and lift motor 11 by means of a clutch 28 therebetween. Thus, at a landing, corrector motor 26 is energized, if the cam group represented by cam 23 does not return to its car stop position, to return that cam to the car stop posi tion by operating against fixed shafts 12 and 21. Advance motor 19 is energized in response to any tendency of the floor selector crosshead to become misoriented during this correcting operation whereby the crosshead is held in its proper position. Inasmuch as this correcting function is performed at each stop of the elevator car, the degree of displacement of the operating cams represented by cam 23 from the car stop position at any stop is at most very slight and is ineffective to disrupt the operation of most of the cams in the group including the cam 23.

As pointed above, the car is stopped at a landing in accordance with this invention by a succession of steps which entail varying the braking force at significant points during the stopping operation and comprise limiting the brakingforce applied to a value which can be utilized conveniently without the brake shoe seizing on the brake drum 15 until the car is completely stopped and thereafter applying a full braking force to insure that the car does not slip.

Such precise variations in the degree of pressure imposed between an electromagnetically actuated brake can be attained advantageously with a brake having a low reluctance magnetic path, a minimum stroke, and a minimum of friction in its moving system. The brake of Fig. I offers these attributes. It is to be noted that Fig. I illustrates only one shoe and its mounting, usually the brake is symmetrical about the drum and includes a diametrically opposed second shoe and mounting, not shown.

A fragment of the machine frame 30 is shown. Clamped to the bed plate 31 of the frame is a base block 32 on which is maintained a machined face 33 of the brake shoe mounting frame 34. The position of the lower portion of frame 34 transverse of the drum axis is adjustable by virtue of the stud 35 extending from base block 32 through lug 36 of frame 34.- Nuts 37 on stud 35 enable the lug 36 to be pulled toward base block 32... When the position of frame '34. is properly adjusted, face 33 is clamped against block 32 by means of bolts38 extending through clearance holes 39 in the base plate 31 and block 32 and into tapped holes 40 inlthe, frame 34. The transverse position of the upper end otthe frames 34 with respect to brake drum 15 is adjusted. by means of a threaded tie rod 41 extending between lugs 42 on the upper ends of respective frames. Nuts.- 43; 'adjustably fix the limits of movement inward while nuts 44 draw lugs 42 inward against nuts 43.

Brake shoe 16 is a portion of a cylinder concentric with brake drum 15. It is provided with a facing 45 of conventional brake lining material. A pair of studs 46. protrude from the outer cylindrical face of the shoe 16. along extensions of. radii of the cylinder and into registering bores 47 in mounting 34. Coil springs 17 mounted in bores 47, embrace protuberances on studs 46, and are maintained in compression by plugs 49 threaded, into the tapped ends of bores 47 to bias the shoes 1,6.inward and engage their linings 45 with brake drum 15. A pair of links 50 pivoted at 51 on opposite sides of frame 34 support each shoe 16 by pivots 52.

In the absence of. appreciable magnetizing forces in the frame 34 and shoe 16, both of which are of ferromagnetic material, the springs 17 force shoe lining 45 against, the drum. The brake releasing electromagnetic forces are developed in a coil 18 which is formed around the arc of frame 34 and inset within a suitable receptacle 54in the frame. In view of the ferromagnetic enclosure and short air gaps between the frame 34 and shoe 16, the'flux generated by passing current through coil 18 has a low reluctance path at allpositions of the shoe. This coupled with the short stroke required of the shoe to engage the brake drum, for example 0.008 inch, and the shoe mounting linkage of two links 50 and four pivots 51 and 52 offering low frictional loads, all enables a magnetic force opposing the brake setting force of the springs 48 to be accurately controlled as a function of current levels in the coil 18. Further, these levels can be designed fora particular structure, and even though confinedto a narrow range of adjustment, the braking system can be held to the tolerances desirable in large scale manufacture without exceeding the economic dictates-of the system in manufacture, installation and maintenance.

Control circuits for the brake are energized from the main leads 61 and 62 connected to a suitable source of direct current, not shown. The brake releasing coil 18 carries varying levels of energizing current depending upon the state of the controls associated therewith. These controls include a main switch timer MT, a main switch M, a Vernier relay VR, 2. low speed up leveling relay 2LU, a low speed down leveling relay 2LD, an up leveling relay LU, a down leveling relay LD, and a brake relay BK. Brake release coil 18 is completely deenergized while a car is standing at a landing inasmuch as the main switch relay M is deenergizing opening its contacts M'1 in lead 64 to disconnect brake release coil 18 from the supply lead 62. At this time, brake relay BK is also deenergized. inasmuch as contact LU-l, LD-Z and 65 are all open to disconnect its actuating coil from supply lead 61.

At the institutiton of a starting operation for the car contacts 65 representing in simplified schematic form the car starting and running circuits controlling relay BK, are closed to energize relay BK thereby closing contacts BK-1, BK-2 and BK-3. Closure of contacts BK-l has no efiect at this time inasmuch as the energizing circuit for the actuating coil VR is open at contacts 66. Contacts 66 represent the portion of the car stopping controls which are actuated at the initiation of a car stopping cycle as in response to the travel of a car to a position where it isassigned to a call. Closure of confacts BK-Z energize relay MT to close the contacts MT-l and thereby energize the main switch relay M. Main relay switchv M; connects the main supply leads 61 and 62 through brake release coil 18 by closing contacts M-.1. The closure of contacts of BK-3 in series with contacts M-1 effectively eliminate current limiting resistor 67 in series with the circuits supplying current to brake release coil- 18. Since relay VR is deenergized at this time, current limiting resistors 68 and 69 are also effectively eliminated from the circuits supplying brake release coil 18 by means of the shunt path provided through leads 71, closed contacts VR-1 and lead 72.

At the time contacts 65 were closed, the advance motor 19 was set in motion, opening advance motor relay contacts AMR, the actuation circuit of which is not shown, to deenergize the leveling relays LD, LU, 2LD and 2LU and initiating the drive of differential output 25 in a manner to displace cam 23. Until cam 23 becomes eifective during the initiation of a car starting operation, the brake release coil 18 carries a current from lead 61 to lead 62 which is limited by resistor 73 in series therewith, protective resistor 74 connected in parallel acrosscoil 18 and resistor 75 connected through cam actuated contacts 76 across coil 18. The value of current flowing through brake release coil 18 with this circuit established is suflicient to displace the brake shoe 16 against the biasing spring 17 and thereby release brake drum 15 for rotation. As the starting operation proceeds, advance motor 19 drives differential 24 to a point where cam 23 on the dilferential output becomes elfective, cam operated contact 76 is opened to disconnect resistor 75 from across the brake release coil 18 and thereby increase the level of current through that coil. Thus, while cam 23 is effective in holding contact 76 open, the current level through coil 18 is substantially above the threshold level required to release the shoe 16 from the drum 15.

When the car is running, brake release coil 18 is shunted by protective resistor 74 and is energized through the series resistor 73 since relays MT, M and BK are all energized. When the car crosshead encounters a row of contacts corresponding to a landing for which a call is registered, the car is assigned to stop for that call and the advance motor is stopped, dropping out advance motor relay AMR to close its contacts to leveling units 77. At this time, contact 66 is also closed by means not shown to energize relay VR and open contacts VR1 whereby resistors 69 and 68 are inserted in series with brake release coil 18 to reduce the level of current flowing through that coil nearly to the point where the springs 17" are permitted to advance the shoe into contact with the brake drum 15. The inductance of brake release coil 18 together with the protective resistor 74 create a circuit which tends to oppose changes in the current level. Accordingly, the change incident to the introduction of additional series resistance across lines 61 and 62 is gradual insofar as the level of current in coil 18 is concerned and therefore the force imposed in opposition to springs 17 reduces only gradually.

As the car approaches the floor at which its crosshead has been stopped, the differential output 25 rotates cam 23 in a manner to permit contact 76 to shunt resistor 75 across brake release coil 18. This additional shunt resistance across coil 18 decreases the voltage across coil 18 and decreases the rate of decline of current therethrough thereby permitting the magnetic force resultant from. that current to decline below the level sufficient to overcome the springs 17. Accordingly, the brake shoe 16 is advanced against the brake drum 15. At this point, the car may be several feet from the landing at which itis to stop. Therefore, sufiicient current is maintained through coil 18 to limit the degree of braking force applied to a level such that the motor can drive the car to the leveling zone through the brake.

The elevator car can be provided with a leveling means utilizing inductor leveling switches of the type disclosed in J. H. Bordens Patent 2,598,214 for Inductor Leveling Switch which issued May '27, 1952. Each switch a:

cludes a permanent magnet which has an air gap between its pole pieces and a movable vane in that air gap which is displaced as the flux density in the gap is varied. The car carries four of these switches vertically spaced from each other so that car motion successively carries them into proximity with a stationary vane of ferromagnetic material in the hatchway as it approaches a landing. Each movable vane carries one of the contacts LLU, LLD, HLU or HLD of the leveling unit 77. For example, if final leveling is to be performed in the last nine inches of travel as a car approaches the landing, the hatchway vane is 18 inches long and is centered with respect to the up switches LLU and HLU and the down switches LLD and HLD so that at the leveling position switches HLU and HLD are open and thus outside the flux modifying influence of the hatchway vane. In the example the switch for HLU would be the uppermost, six and one-quarter inches below that and three inches above the middle of the vane when the car is leveled would be switch LLU, six inches below LLU would be LLD and six and one-quarter inches below LLD would be HLD. Thus, as an up traveling car approaches a landing HLU is closed when the car is 18%, inches from the landing, LLU closes when it is about 12 inches from the landing, LLD closes when it is about 6 inches from the landing and HLU reopens when the car is within A inch of the landing. On approaching a landing from above the sequence is inverted and HLD operates followed by LLD and LLU and then by the reopening of HLD.

If an up traveling car is assumed to be responding to a call, HLU is closed when the hatchway vane enters the flux path for the switch of contact HLU and alters the flux in that path sufliciently to enable HLU to be drawn closed, thereafter relay LU is energized to close contact LU-1 and thereby complete a circuit from lead 61 through lead '78, contacts LD-l and LU-l and brake relay coil BK. At this time, contact 65 which was closed when the car was started is opened by means not shown and is maintained open thereafter until the car is completely stopped so that the control of the brake relay is effected by leveling relay contacts.

The car continues to move toward the leveling position at the landing for which the stop is being made by virtue of the drive of motor 11 despite the presence of some braking force introduced by the engagement of brake drum15 by brake shoe 16. As the car comes closer to the landing,v for example when in about 12 inches below the landing on an up trip, contact LLU of leveling unit 77 closes in the same manner that HLU is closed to energize relay 2LU and close its contact 2LU-1. This increases the current supplied to brake release coil 18 to a level sufficient to relieve essentially all of the braking force developed between brake drum 15 and brake shoe 16 whereby relative motion between those elements is continued without seizing despite the reduced speed during the final leveling. Advantageously, the shoe 16 is not disengaged from drum 15 since it is desirable to avoid reengagement during final stopping which would otherwise be required and thus the possibility of seizing at that time. Increased currents to the brake coil is realized by shunting out a portion of the resistance in series with the brake coil, specifically by shunting out resistor 69 by means of the shunt path provided through contact 2LU-1. The car therefore continues to move toward its final position.

When the car is level with the floor, contacts HLU of leveling unit 77 open deenergizing relay LU to open contacts LU-l and thus break the circuit energizing brake relay BK. Brake-relay BK opens its contacts BK-3 to insert additional resistance in series with brake release coil 18 sufficient to enable that coil to develop a braking force adequate to hold 100 percent of the rated car. capacity. This braking force rapidly brings the car to a halt. Since the car is moving 'at a slow speed, it is halted within an additional half inchof movement whereby it is held level with the floor and the lifting motor field is deenergized. At this time,;contactsBK-1 arealso open to deenergize relay VR and close-its contacts: VR-l to shunt series resistors 68 and 69. The magnitude of these resistors is considerably less than the magnitude of brake resistor 67 so that brake resistor 67 in addition to replacing the now shunted resistors 68- and 69 imposes the additional resistance necessary to effect the requisite braking level.

Contacts BK-Z upon opening deenergize main switch timer relay MT which is of the slow drop out or flux decay type. After a suitable timing interval, for example several tenths of a second, contacts MT1 open to deenergize main switch relay M and thereby completely disconnect brake holding coil 18 from line 62 by opening contacts M-l. At this time, the full braking force is ap plied to the lifting mechanism. However, thecar is no longer in motion and therefore no difficulty is experienced in abruptly stopping the car as heretofore has been inci-" dent to the seizure of drum 15 by shoe' 16.

Thus, at the initiation of the stopping cycle first and second resistors 68 and 69 are inserted in series with the brake release coil 18 to reduce the current level therein gradually as the current follows an exponential function determined by the magnitude of resistance 74 and impedance of coil 18. In one embodiment this reduction is to a level which is below that maximum present when the car is running by about percent of the difierence ing, the current level in coil 18 is decreased by inserting, a fourth series resistor 67 in series with the coil to .impose a braking force sutficient to hold the car when .the

lifting motor is deenergized. After the car has reached the leveling position and the holding level of braking has been imposed the braking force is increased further by an additional reduction of current through coil 18 aslby opening the circuit to the current source at contacts M-l.

It is to be noted that the lifting motor 11 maintains. control of the position of the elevator car until it has 1eveled at the floor and the doors have started to open. Ordinarily, door opening is initiated at the time thesec. ond leveling relays are energized or while the car is still. several inches from its final level position. However, the doors do not attain their fully open position until shortly after brake relay BK has dropped out in the illustrative embodiment and ordinarily the brake is fully set by the opening of relay contact M1 prior to the conditioning of the car doors for the reception of any additional load. Accordingly, a car loaded to capacity will be required to level at the floor by virtue of the operation of the lifting motor. Further, once it is stopped at the floor it is held by a braking force corresponding to its capacity and has its lifting motor deenergized. It will not be conditioned for the reception of an additional load until after the full braking force has been applied and therefore will not tend to sag with respect to the leveling position as a result of any added load at that floor. Accordingly, smooth stopping is achieved with the disclosed system while affording a braking level substantially in excess of the rated car capacity during the critical period when such level is required, namely, while the lifting motor-is unavailable for maintaining or achieving the desired a e tion of the car at the landing. V

While it is not necessary to describe in detail the level ing; operation of the: motor since a number; ofleveling systems are available for use with the proposed: brake control, it should be noted that. if" the car advances be? yond the floor on 'an up trip contact HLD will be closed to. energize relayLD. and thereby institute a-downward movement under the control of lifting motorl l. to an appropriate position withrespect to thealanding. Under such circumstances, the energization of relay LD while relay LU is deenergized' will energize the brakerelay through contacts LD-2 and LU -2 8d that the braking level corresponding to 100-.percen'tof'car capacity will be relieved until the car again is leveled at the landing.

' Restarting of the car insofar as the brake controls are concerned is effected as described above by the closure of contact 65, by means notshown, to'energize brake relay BK, main switch relay- M, and thus brake release coil 18 while the lifting motor is brought into operation to assume the load of the car.

Similarly, a downward traveling car effects a stopping sequence as described by first energizing relay VR through the closure of contacts 66. Such contacts reopen upon or prior to the closure of contacts 65 in the starting operation, all by means not shown. Further, in the sequence of stoping on a down trip, contacts 76' are closed to bring the brake shoe 16 into contact with brake drum 15. Leveling while traveling downward is effected by first closing contacts HLD through the now closed'advance motor relay contacts AMR to energize relay LD and, thereafter, when the car is at a position closer to the floor, by closing contacts LLD to reenergize relay 2L1) whereupon the braking force is relieved without lifting the shoe free of the drum 15 during the latter portion of the stopping cycle. The final stopping motion is efiected during the last half inch of car travel by the deenergization of relay LD to open the brake relay circuit and to reduce the level of current in the brake release coil 18 to a level normally sufficient to "establish and maintain the car position. On. a downward trip brake relay BK also controls the operation ofmainswitch timer MT to deenergize main switch relay M a short interval after the energization of thebrake relay and effect application of the entire braking force'through the removal of all current from brake release coil-18.

In one example of an operative brake control wherein the car was counterweighted to 40 percent of full load and the brake was rated at 125 percent of full load less the counterweighted portion of that load, the brake coil utilized had 117 ohms of resistance- Protective resistor 74 Was of 1000 ohms resistance and damping resistor 75 Was 175 ohms. Limiting resistor 73. was of 70 ohms resistance. Resistor 69 was of 37 ohms resistance. Resistor 68 was of 75 ohms resistance and resistor 67 was of 152 ohms resistance. The circuit was supplied from a three-phase full wave rectifier fed by 180 volts R.M.S.

It is to be appreciated that other circuits can be utilized wherein a car can be brought to a halt by utilizing a braking force corresponding to 10.0 percent of car capacity less the counterweighted portionofthe load and, subsequent to the cessation of movement, an additional braking force a plied. or wherein other than the maximum force can be applied to bring the car to a halt and subsequent to the stopping of the car a fullbraking force a plied in order to enhance the operating characteristics of the car. Thus, this concept can be utilized in other than a preset brake of the type illustrated here. Specific'ally, it might be applied to a system wherein the-brake is set only during the last half inch of movement as described with respect to the deenergizationof the leveling relays LD or LU. In any of these systems a timing or other measuring means insuring that the car is fully stopped can be employed to applythe total braking force. This determination of the instant at which total braking force is applied might also be established by a motion sensing device or some other elements such as a relay in 16 themotor field circuits indicating that the motor has been completely deenergized to establish the maximum braking level required to fix the position ofthe' car during any additional loading.

This invention lends itself to applications and systems other than those proposed herein. For example, while the brake control system has been illustrated with an elevator system having a commutator type floor selector machine other types of car control mechanisms can be employed and sequencing'of the brake control can be actuated from appropriate elements of these .known mechanisms paralleling the discussed elements in function With respect to time or car position. Accordingly, it is to be understood that these disclosures areto be read as exemplary and not in a limiting sense since one skilled in the art might readily adapt the teachings, of this invention to such other systems without departing from its spirit or scope.

What is claimed is:

1. In an elevatorsystem, a car having a rated capacity, a brake, means to apply a braking force of a first level sufiicient to hold the car when capacity loaded, a timer defining an interval from the operation of said brake applying means, and means to apply a braking force of a level substantially in excess of said first level upon the expiration of said interval.

2. In an elevator system, a car having a rated capacity, a brake, means to apply a braking force to stop said carwhich is about one hundred percent of the uncounterweighted portion of the car and load Weight when loaded at rated capacity, a'tim'er defining an interval from the operation of said brake applying means, and means to apply a braking force upon the expiration of said interval which is sufficient to hold a car loaded to about one hundred and twenty-five percent of rated capacity.

3. In an elevator system, a car, a landing served by said car, driving means for said car, a brake for said car having a capacity in excess of the uncounterweighted portion of the rated load capacity of the car, means to apply a braking force through said brake which substantially corresponds to the uncounterweighted portion of the rated capacity of said car when saidv car is substantially level with said landing in order to stop said car, and means to apply the full capacity of said brake to said car after said car has stopped.

4. In an elevator system, a car, a landing served by said car, driving means for said car, a brake for said car having a capacity in excess of the uncounterweighted portion of the rated capacity of the car, meanszto apply a first braking force to the car through said brake which substantially corresponds to the uncounterweighted portion of the rated capacity of said car when said car is level with said landing, means to define an interval following the application of said first braking force, and means to apply the full capacity of said brake upon ter mination of said interval.

5. In an elevator system, a'car having a rated capacity, a brake drum for said car, a brake shoe cooperating with said drum, a control for said car, means to initiate advancement of said brake shoe towardsaid drum in response to said control, means to engage said shoe with said drum and develop a braking force in response to said control, means to reduce said braking force assaid car is retarded, means to increase said braking force as the car closely approaches a landing to a level which is about that required to hold a capacity loaded car, and means to further increase the braking force subsequent to the stopping of a car.

6. In an elevator system, a car, a landing served by saidcar, driving means for said car, a brake for said car having a capacity in excess of the uncounterweighted portion of the rated load capacity of the car, means to initiate braking of said car at a first level of braking force in advance of its arrival at said landing, means to reduce braking of said car from said first level of brakmg force during the slowing of said car as it approaches said landing, means to apply a braking force to said car through said brake which substantially corresponds to the uncounterweighted portion of the rated capacity of said car when said car is essentially level with said landing, and means to apply the full capacity of said brake to said car after said car has stopped.

7. In an elevator system, a car, a landing served by said car, driving means for said car, a brake for said car having a capacity in excess of the uncounterweighted portion of the rated load capacity of the car, means to initiate braking of said car by applying thereto a first level of braking force in advance of its arrival at said landing, means to reduce the level of braking force applied to said car from said first level during the slowing of said car for a stop at said landing, means to apply a braking force to said car through said brake which substantially corresponds to the uncounterweighted portion of the rated capacity of said car when said car is essentially level with said landing, means to define an interval following the application of said last mentioned braking force, and means to apply the full capacity of said brake upon the termination of said interval.

8. In an elevator system, a car, a landing served by the car, a car drive, a brake drum connected to said car drive, a brake shoe arranged for engagement with said drum, a spring biasing said brake shoe for engagement with said drum, a solenoid arranged to develop a force opposing the force of said spring, a source of electrical current, and a circuit'for controlling the level of current from said source to said solenoid in a range between zero and a level utilized to lift said shoe free of said drum comprising means for establishing a maximum current level sufficient to lift said shoe free from said drum while said car is running, means to reduce said solenoid current to a first intermediate load to permit the displacement of said shoe toward said drum effective at the initiation of a stop of said car at said landing, said first intermediate current level being below said maximum level by about eighty percent of the difference between said maximum level and the level at which said spring overcomes said solenoid force to engage said shoe with said drum, means effective during the initial portion of a stopping interval for gradually reducing said current from said first intermediate level to a second intermediate level below the current level permitting engagement of said shoe with said drum, means effective subsequent to establishment of said second intermediate level of current for increasing said current from said second intermediate level to a third intermediate level developing a force in said solenoid approaching a balance with the force of said spring, means effective when said car is essentially level with said landing for decreasing said current from said third intermediate level to a fourth intermediate level below said first three intermediate levels and sufiicient to enable said spring to bias said shoe against said drum with sufficient force to sustain a capacity loaded car, a timer, means to initiate a timing of said timer when said car is stopped, and means to decrease said current through said solenoid at the termination of an interval measured by said timer whereby a braking force substantially in excess of that required to sustain a capacity loaded'car is applied between said shoe and said drum.

9. A brake control for an elevator comprising a brake drum, a spring applied brake shoe cooperating with said drum, a source of electrical current, a solenoid arranged to Oppose the force of the brake shoe spring when energized by current from said source, a first and second resistor connected in series with said source andisaid solenoid during the initial portion of a car stopping operation, a third resistor connected across said solenoid during a stopping operation and subsequent to the connection of said first and second resistors, means to effectively eliminate said first resistor from the series circuit including said source and said solenoid subsequent to the application of said third resistor, a fourth resistance, means to connect said-.fourthzresistance in series with said solenoid and said source to reduce the force opposing the application of said brake shoe to said drum to a level which brings said elevator to a stop, and means to disconnect said solenoid from said source subsequent to the operation of said fourth resistance inserting means.

10. In a brake control for an elevator, a brake drum,

a brake shoe, a spring arranged to bias said brake shoe toward said brake drum, a solenoid arranged when energized to oppose theforce of said spring, a source of electrical current, a first, and second resistor each of a lower order of magnitude of resistance than the resistance of said solenoid and connected in series with said source and said solenoid, a shunt connected across said first and second resistors, means to open said shunt at the initiation of a brake setting cycle, a third resistor of the same order of magnitude as said solenoid resistance, means to connect said third resistor across said solenoid during the initial portion of a brake setting cycle whereby said solenoid current is gradually reduced to a level developing a force permitting said spring to carry said shoe into contact with said drum, a second shunt, means to connect said second shunt across said first resistor as the elevator reaches a predetermined point in its travel, a fourth resistance of a magnitude exceeding the sum of said first and second resistances, means to insert said fourth resistance in series with said solenoid and said source and to initiate a timing operation, and means to disconnect said solenoid from said source at the termination of said timing operation.

,11. In an elevator system, a car, a landing served by the car, a car drive, a brake drum connected to said drive, a brake shoe arranged for engagement with said drum, a spring biasing said brake shoe for engagement with said drum, a solenoid for opposing said spring whereby the braking force developed between said brake drum and said brake shoe is an inverse function of the current in said solenoid, a first resistance connected across said solenoid to control the rate of change of current flow therein, first means for inserting resistance in series with said solenoid and said source to reduce the current therethrough in response to the initiation of a brake setting cycle, second means for connecting resistance in parallel with said solenoid to reduce the current therethrough and increase the rate of change of current fiow therein subsequent to the operation of said first means, third means effective as said car enters a low speed leveling zone adjacent said landing for re ducing the resistance in series with said solenoid to in crease the current therethrough at said increase rate to a level relieving essentially all pressure of said shoe on said drum, fourth means effective when said car is essentially at the level of the landing at which it is to stop for increasing the resistance in series with said sole noid to decrease the current therein at said increased rate 'to a level sufficient tostop said car, and a fifth means for opening the circuit between said solenoid and said source after said car has been stopped to apply the full brake.

12. In an elevator system, an elevator car, lifting mechanism for said car, braking means associated with said lifting mechanism, means to apply a braking force. through said braking means sufiicient to bring the car to a stop at a predetermined point in its travel, timing means oper ated in conjunction with the braking means to define an interval which expires subsequent to the stopping of the car and means effective on the expiration of said inter val toactuate said braking means and increase the level of braking force.

13. A brake for anelevator car including a brake drum, a brake shoe, a spring biasing said shoe toward said drum, means for opposing the biasing force of said spring, means to actuate said opposing means to a level 13 sufiicient to lift and maintain said shoe free of said drum while said car is in motion, means to reduce the force of said opposing means to approach the threshold level necessary to sustain said shoe free of said drum in response to the initiation of the car stopping operation, means to further reduce the force in said opposing means to a level substantially below that required to overcome said spring force when said car is a first given distance from a stopping point, means for increasing the force of said opposing means to a level closely approaching a balance with said spring force when said car is a second given distance from the stopping point which is closer thereto than said first given distance and means for reducing the force of said opposing means to a level at which said spring force exceeds said opposing means force by an amount sufficient to stop said car when said car enters a stopping range bounding said stopping point.

14. A brake for an elevator car including a brake drum, a brake shoe, a spring biasing said shoe toward said drum, a brake solenoid arranged to oppose the biasing force of said spring and to lift said shoe free of said drum, a source of electrical current means to connect said solenoid across said current source, means to reduce the current in said solenoid to approach the threshold level necessary to sustain said shoe free of said drum in response to the initiation of the car stopping operation, means to further reduce the current in said solenoid to a level substantially below that required to overcome said spring force when said car is a first given distance from a stopping point, means for increasing the current in said solenoid to a level generating a force closely approaching a balance with said spring force when said car is a second given distance from the stopping point which is closer thereto than said first given distance and means for reducing the current in said solenoid to a level at which said spring force exceeds said solenoid force by an amount sufiicient to stop said car when said car enters a stopping range bounding said stopping point.

No references cited. 

